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11 pages, 4096 KiB

Open AccessArticle

Experimental Investigation and Numerical Simulation of a Self-Wiping Corotating Parallel Octa-Screw Extruder

by Cheng-Ying Liu, Shota Mikoshiba, Yutaka Kobayashi, Akira Ishigami, Daisuke Yorifuji, Shin-ichiro Tanifuji and Hiroshi Ito

Polymers 2022, 14(6), 1201; https://doi.org/10.3390/polym14061201 - 16 Mar 2022

Cited by 2 | Viewed by 2799

Abstract

An octa-screw extruder (OSE) is equipment for pelletizing, blending, and mixing polymers and composites. In this study, the degree of resin filling, residence time distribution (RTD) of molten resin, and temperature profile in the octa-screw extruder were evaluated both experimentally and numerically. An [...] Read more.

An octa-screw extruder (OSE) is equipment for pelletizing, blending, and mixing polymers and composites. In this study, the degree of resin filling, residence time distribution (RTD) of molten resin, and temperature profile in the octa-screw extruder were evaluated both experimentally and numerically. An intermeshing corotating parallel octa-screw kneading extruder was used for the experiments. For the comparison study, the results obtained from this extruder were compared with the twin-screw extruder. High-density polyethylene was selected as the material for extrusion. Meanwhile, a numerical code, based on a 2.5 D finite element method derived from the Hele–Shaw flow model, was developed to simulate the octa-screw extrusion process. The empirical outcomes suggest that octa-screw extrusion exhibited a narrower RTD of the molten resin compared with the twin-screw extrusion, suggesting better extrudate quality. The octa-screw extrusion also showed a lower temperature profile than twin-screw extrusion. The results of the simulation were also found to be in good agreement with experimental measurements. Experimental and numerical investigations of an OSE enable detailed comprehension and visualization of resin distribution in the entire length of the OSE, thus providing advantages in terms of process optimization. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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32 pages, 5667 KiB

Open AccessArticle

Macromolecular Insights into the Altered Mechanical Deformation Mechanisms of Non-Polyolefin Contaminated Polyolefins

by Ruben Demets, Marie Grodent, Karen Van Kets, Steven De Meester and Kim Ragaert

Polymers 2022, 14(2), 239; https://doi.org/10.3390/polym14020239 - 7 Jan 2022

Cited by 13 | Viewed by 2972

Abstract

Current recycling technologies rarely achieve 100% pure plastic fractions from a single polymer type. Often, sorted bales marked as containing a single polymer type in fact contain small amounts of other polymers as contaminants. Inevitably, this will affect the properties of the recycled [...] Read more.

Current recycling technologies rarely achieve 100% pure plastic fractions from a single polymer type. Often, sorted bales marked as containing a single polymer type in fact contain small amounts of other polymers as contaminants. Inevitably, this will affect the properties of the recycled plastic. This work focuses on understanding the changes in tensile deformation mechanism and the related mechanical properties of the four dominant types of polyolefin (PO) (linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP)), contaminated with three different non-polyolefin (NPO) polymers (polyamide-6 (PA-6), polyethylene terephthalate (PET), and polystyrene (PS)). Under the locally elevated stress state induced by the NPO phase, the weak interfacial adhesion typically provokes decohesion. The resulting microvoids, in turn, initiate shear yielding of the PO matrix. LLDPE, due to the linear structure and intercrystalline links, is well able to maintain high ductility when contaminated. LDPE shows deformation similar to the pure material, but with decreasing ductility as the amount of NPO increases. Addition of 20 wt% PA-6, PET, and PS causes a drop in strain at break of 79%, 63%, and 84%, respectively. The typical ductile necking of the high-crystalline HDPE and PP is strongly disturbed by the NPO phase, with a transition even to full brittle failure at high NPO concentration. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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15 pages, 4391 KiB

Open AccessArticle

Effects of Dynamic Crosslinking on Crystallization, Structure and Mechanical Property of Ethylene-Octene Elastomer/EPDM Blends

by Yuan-Xia Wang, Chen-Chen Wang, Ying Shi, Li-Zhi Liu, Nan Bai and Li-Fu Song

Polymers 2022, 14(1), 139; https://doi.org/10.3390/polym14010139 - 30 Dec 2021

Cited by 12 | Viewed by 3231

Abstract

The dynamic crosslinking method has been widely used to prepare rubber/plastic blends with thermoplastic properties, and the rubber phase is crosslinked in these blends. Both polyolefin elastomer (POE) and ethylene-propylene-diene monomer rubber (EPDM) can be crosslinked, which is different from usual dynamic crosslinking [...] Read more.

The dynamic crosslinking method has been widely used to prepare rubber/plastic blends with thermoplastic properties, and the rubber phase is crosslinked in these blends. Both polyolefin elastomer (POE) and ethylene-propylene-diene monomer rubber (EPDM) can be crosslinked, which is different from usual dynamic crosslinking components. In this paper, dynamic crosslinked POE/EPDM blends were prepared. For POE/EPDM blends without dynamic crosslinking, EPDM can play a nucleation role, leading to POE crystallizing at a higher temperature. After dynamic crosslinking, the crosslinking points hinder the mobility of POE chains, resulting in smaller crystals, but having too many crosslinking points suppresses POE crystallization. Synchrotron radiation studies show that phase separation occurs and phase regions form in non-crosslinked blends. After crosslinking, crosslinking points connecting EPDM and part of POE chains, enabling more POE to enter the EPDM phase and thus weakening phase separation, indicates that dynamic crosslinking improves the compatibility of POE/EPDM, also evidenced by a lower β conversion temperature and higher α conversion temperature than neat POE from dynamic mechanical analysis. Moreover, crosslinking networks hinder the crystal fragmentation during stretching and provide higher strength, resulting in 8.3% higher tensile strength of a 10 wt% EPDM blend than neat POE and almost the same elongation at break. Though excessive crosslinking points offer higher strength, they weaken the elongation at break. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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13 pages, 3631 KiB

Open AccessArticle

Crystallization of Isotactic Polypropylene Nanocomposites with Fibrillated Poly(tetrafluoroethylene) under Elevated Pressure

by Przemyslaw Sowinski, Sivanjineyulu Veluri and Ewa Piorkowska

Polymers 2022, 14(1), 88; https://doi.org/10.3390/polym14010088 - 27 Dec 2021

Cited by 6 | Viewed by 3318

Abstract

Nanocomposites of isotactic polypropylene with 1–5 wt.% of fibrillated PTFE (PP/T) were prepared, and their crystallization during cooling under elevated pressure, in a wide pressure range, up to 300 MPa, as well as the resulting structure, were examined. The crystallization peak temperatures of [...] Read more.

Nanocomposites of isotactic polypropylene with 1–5 wt.% of fibrillated PTFE (PP/T) were prepared, and their crystallization during cooling under elevated pressure, in a wide pressure range, up to 300 MPa, as well as the resulting structure, were examined. The crystallization peak temperatures of PP/T, especially with 3 and 5 wt.% of PTFE, exceeded by up to 13 °C those of neat PP. Moreover, a fine-grain structure was formed in PP/T in the entire pressure range, which proved the ability of the fibrillated PTFE to nucleate crystallization of PP in the γ-form under elevated pressure. This also resulted in a higher crystallinity level developed in the γ-domain, before the temperature range of the α-domain was reached during cooling. Hence, the γ-content increased in comparison to that in neat PP, under the pressure up to 200 MPa, especially under 50–100 MPa. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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12 pages, 1976 KiB

Open AccessArticle

Influence of Solvent and Substrate on Hydrophobicity of PLA Films

by Verónica Luque-Agudo, Amparo M. Gallardo-Moreno and María Luisa González-Martín

Polymers 2021, 13(24), 4289; https://doi.org/10.3390/polym13244289 - 8 Dec 2021

Cited by 12 | Viewed by 4469

Abstract

The study of the surface properties of materials is key in determining whether the material will be suitable for medical purposes. One of these properties is hydrophobicity, which is important when assessing its behavior against bacterial adhesion. In this work, we have studied [...] Read more.

The study of the surface properties of materials is key in determining whether the material will be suitable for medical purposes. One of these properties is hydrophobicity, which is important when assessing its behavior against bacterial adhesion. In this work, we have studied the influence of the solvent (chloroform, acetone, and tetrahydrofuran) and the substrate (glass, PTFE, silicone, and Ti6Al4V) on which polylactic acid is deposited in solution to manufacture films by solvent-casting. Thus, it has been found that there are no significant differences in hydrophobicity and surface tension among the solvents evaluated, but there are significant differences with respect to the substrates: PLA films casted on silicone are hydrophobic, while those casted on the rest of the substrates are hydrophilic. This is related to the fact that the silicone interacts with the polymer modifying its spatial arrangement, exposing its methyl groups towards the interface with the air. In this way, it has been shown that, when manufacturing PLA films, it is important to choose the right surface on which to deposit them, depending on their desired function. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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18 pages, 7755 KiB

Open AccessArticle

Constitutive Modelling of Polylactic Acid at Large Deformation Using Multiaxial Strains

by John Sweeney, Paul Spencer, Glen Thompson, David Barker and Phil Coates

Polymers 2021, 13(17), 2967; https://doi.org/10.3390/polym13172967 - 31 Aug 2021

Cited by 2 | Viewed by 2602

Abstract

Sheet specimens of a PLLA-based polymer have been extended at a temperature near to the glass transition in both uniaxial and planar tension, with stress relaxation observed for some time after reaching the final strain. Both axial and transverse stresses were recorded in [...] Read more.

Sheet specimens of a PLLA-based polymer have been extended at a temperature near to the glass transition in both uniaxial and planar tension, with stress relaxation observed for some time after reaching the final strain. Both axial and transverse stresses were recorded in the planar experiments. In all cases during loading, yielding at small strain was followed by a drop in true stress and then strain hardening. This was followed by stress relaxation at constant strain, during which stress dropped to reach an effectively constant level. Stresses were modelled as steady state and transient components. Steady-state components were identified with the long-term stress in stress relaxation and associated with an elastic component of the model. Transient stresses were modelled using Eyring mechanisms. The greater part of the stress during strain hardening was associated with dissipative Eyring processes. The model was successful in predicting stresses in both uniaxial and planar extension over a limited range of strain rate. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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12 pages, 3415 KiB

Open AccessArticle

Layer-by-Layer (LbL) Surface Augmented Modification of Poly(Styrene/Divinylbenzene)High Internal Phase Emulsion for Carbon Dioxide Capture

by Muhammad Imran Azman, Jirasuta Chungprempree, Jitima Preechawong, Pornsri Sapsrithong and Manit Nithitanakul

Polymers 2021, 13(14), 2247; https://doi.org/10.3390/polym13142247 - 9 Jul 2021

Cited by 3 | Viewed by 3280

Abstract

In this study, we used amines electrolyte solution with layer-by-layer (LbL) technique to modify and increase the CO₂ adsorption capacity of highly porous polymer from high internal phase emulsion template polymer. This perspective presents the extraordinary versatility of emulsion templating polymerization, which [...] Read more.

In this study, we used amines electrolyte solution with layer-by-layer (LbL) technique to modify and increase the CO₂ adsorption capacity of highly porous polymer from high internal phase emulsion template polymer. This perspective presents the extraordinary versatility of emulsion templating polymerization, which has emerged with the growing numbers of HIPE systems and modification. In this study, we used polyHIPE prepared from styrene (S) and divinylbenzene (DVB) with varying ratios; 80:20, 20:80, and 0:100 to improve the surface area, thermal properties, and mechanical properties of the materials. Furthermore, the surface of the polyHIPE was modified by LbL technique to increase the adsorption efficiency. This technique consisted of two main layers, the primary layer of poly(diallyldimethylammonium chloride) (PDADMAC) and polystyrene sulfonate (PSS) and the secondary layer, which was the CO₂ adsorbing layer, of polyethylene imine (PEI) or tetraethylene pentamine (TEPA). Poly(S/DVB)HIPE modified by PEI terminated as the secondary coating showed the highest CO₂ adsorption capacity, with up to 42% (from 0.71 to 1.01 mmol/g). The amine-multilayered modified material still possessed an open cell structure, since the solution did not block the pore structure of the poly(S/DVB)HIPE and was suitable for being used as an adsorbent in adsorption technology. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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13 pages, 4985 KiB

Open AccessArticle

Migration Behavior of Lubricants in Polypropylene Composites under Accelerated Thermal Aging

by Mun-Gyu Bak, Jong-Sung Won, Seon-Woong Koo, Arom Oh, Han-Ki Lee, Dae-Sik Kim and Seung-Goo Lee

Polymers 2021, 13(11), 1723; https://doi.org/10.3390/polym13111723 - 25 May 2021

Cited by 6 | Viewed by 4490

Abstract

The surface migration of lubricants degrades the quality of thermoplastic polymer composites. In this study, the surface migration of lubricants in polypropylene composites were studied to improve the quality of the composites. Polypropylene (PP)/lubricant composites were manufactured using a co-rotating twin-screw extruder and [...] Read more.

The surface migration of lubricants degrades the quality of thermoplastic polymer composites. In this study, the surface migration of lubricants in polypropylene composites were studied to improve the quality of the composites. Polypropylene (PP)/lubricant composites were manufactured using a co-rotating twin-screw extruder and injection molding, and the migration phenomena of the lubricant in the PP/lubricant composites were investigated under accelerated aging conditions with temperatures in the range of 20 to 90 °C and humidity of 100% for 72 h. The interrelation between the surface migration properties of PP/lubricant composites were investigated by considering their microstructural and morphological features, which were influenced by the thermal aging conditions. Further, the microstructural and morphological features were examined by contact angle, surface energy, attenuated total reflectance Fourier-transform infrared spectrometry, X-ray photoelectron spectroscopy, close-up digital imaging, and atomic force microscopy analyses. The polypropylene composites containing the magnesium stearate as the lubricant were found to exhibit a more stable migration behavior than the polypropylene composites containing a calcium stearate lubricant. This is attributed to multiple synergistic factors, such as interfacial tension and work of adhesion between PP and the lubricant. The findings of this study can be utilized to effectively manufacture high-quality thermoplastic composites for the fourth industrial revolution. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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11 pages, 4395 KiB

Open AccessArticle

Thermoelectric Generator Using Polyaniline-Coated Sb₂Se₃/β-Cu₂Se Flexible Thermoelectric Films

by Minsu Kim, Dabin Park and Jooheon Kim

Polymers 2021, 13(9), 1518; https://doi.org/10.3390/polym13091518 - 9 May 2021

Cited by 18 | Viewed by 3996

Abstract

Herein, Sb₂Se₃ and β-Cu₂Se nanowires are synthesized via hydrothermal reaction and water evaporation-induced self-assembly methods, respectively. The successful syntheses and morphologies of the Sb₂Se₃ and β-Cu₂Se nanowires are confirmed via X-ray powder diffraction [...] Read more.

Herein, Sb₂Se₃ and β-Cu₂Se nanowires are synthesized via hydrothermal reaction and water evaporation-induced self-assembly methods, respectively. The successful syntheses and morphologies of the Sb₂Se₃ and β-Cu₂Se nanowires are confirmed via X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), and field emission transmission electron microscopy (FE-TEM). Sb₂Se₃ materials have low electrical conductivity which limits application to the thermoelectric generator. To improve the electrical conductivity of the Sb₂Se₃ and β-Cu₂Se nanowires, polyaniline (PANI) is coated onto the surface and confirmed via Fourier-transform infrared spectroscopy (FT-IR), FE-TEM, and XPS analysis. After coating PANI, the electrical conductivities of Sb₂Se₃/β-Cu₂Se/PANI composites were increased. The thermoelectric performance of the flexible Sb₂Se₃/β-Cu₂Se/PANI films is then measured, and the 70%-Sb₂Se₃/30%-β-Cu₂Se/PANI film is shown to provide the highest power factor of 181.61 μW/m·K² at 473 K. In addition, a thermoelectric generator consisting of five legs of the 70%-Sb₂Se₃/30%-β-Cu₂Se/PANI film is constructed and shown to provide an open-circuit voltage of 7.9 mV and an output power of 80.1 nW at ΔT = 30 K. This study demonstrates that the combination of inorganic thermoelectric materials and flexible polymers can generate power in wearable or portable devices. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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12 pages, 4946 KiB

Open AccessArticle

Nanosized SnO₂ Prepared by Electrospinning: Influence of the Polymer on Both Morphology and Microstructure

by Alberto Rubin Pedrazzo, Claudio Cecone, Sara Morandi, Maela Manzoli, Pierangiola Bracco and Marco Zanetti

Polymers 2021, 13(6), 977; https://doi.org/10.3390/polym13060977 - 23 Mar 2021

Cited by 16 | Viewed by 2894

Abstract

An electrospinning (ES) procedure of polymeric solutions containing metal oxide precursors, followed by thermal treatments, was exploited to obtain SnO₂ nanofibers. Attention was focused on the effect of different templating polymers (polyvinyl pyrrolidone (PVP), polyethylene oxide (PEO) and polyvinyl acetate (PVAc)) on [...] Read more.

An electrospinning (ES) procedure of polymeric solutions containing metal oxide precursors, followed by thermal treatments, was exploited to obtain SnO₂ nanofibers. Attention was focused on the effect of different templating polymers (polyvinyl pyrrolidone (PVP), polyethylene oxide (PEO) and polyvinyl acetate (PVAc)) on the morphologies and particle size distributions of SnO₂. We demonstrated that with different polymers, the final oxide’s morphology and crystallite size change. Defined fibers, with homogeneous diameter, were obtained with each polymer, but, after calcination, the morphology of the oxide changes, leading to fibers, “flakes” or “sphere-shaped” particles when PVP, PEO or PVAc were used, respectively, as evidenced by SEM images. Data from HR-TEM and XRD measurements confirm that SnO₂ samples consist of crystalline cassiterite, with small mean particle dimensions calculated by Debye–Scherrer equation, i.e., 30, 11 and 25 nm with PVP, PEO and PVAc, respectively. TEM measurements put in evidence lower average particle sizes and for SnO₂ obtained with PEO average size of 8.5 nm with a standard deviation of ±4.9 nm was evidenced. By applying different calcination temperatures on fiber mat obtained by the same polymer, i.e., PEO, the influence of polymer not only on the final shape of the oxide particles but also on the crystallite size was definitively demonstrated. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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20 pages, 5812 KiB

Open AccessArticle

Creep Response of Carbon-Fiber-Reinforced Composite Using Homogenization Method

by Mostafa Katouzian and Sorin Vlase

Polymers 2021, 13(6), 867; https://doi.org/10.3390/polym13060867 - 11 Mar 2021

Cited by 10 | Viewed by 2669

Abstract

The homogenization theory, used for the study of differential equations with periodic coefficients, with a rapid variation, is used in the paper for the analysis of the creep phenomenon of composite materials, reinforced with fibers. Generally, a polymer composite having a matrix with [...] Read more.

The homogenization theory, used for the study of differential equations with periodic coefficients, with a rapid variation, is used in the paper for the analysis of the creep phenomenon of composite materials, reinforced with fibers. Generally, a polymer composite having a matrix with a viscoelastic response manifests a creep behavior. A good knowledge of mechanical constants allows us to predict the time response under the action of a load, which is important in engineering. The homogenization method is used to determine the engineering constants for a composite reinforced with carbon fibers. The method is applied for the particular case of fiber-reinforced unidirectional composites to obtain the equations that finally offer the required values. The epoxy matrix Fibredux 6376C is reinforced with carbon fibers T800 and the thermoplastic specimens made by APC2 material is reinforced with carbon fibers of the type IM6. The experimental results give a good concordance with the theoretical predictions. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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19 pages, 5674 KiB

Open AccessArticle

Fused Filament Deposition of PLA: The Role of Interlayer Adhesion in the Mechanical Performances

by Sara Liparoti, Daniele Sofia, Aldo Romano, Francesco Marra and Roberto Pantani

Polymers 2021, 13(3), 399; https://doi.org/10.3390/polym13030399 - 27 Jan 2021

Cited by 23 | Viewed by 2527

Abstract

A set of criteria to enhance mechanical performances of standard specimens (Type V, ANSI D368) made of polylactic acid (PLA) were proposed. Fused PLA deposition was conducted with nozzle temperature ranging from 180 to 230 °C and deposition plate temperature ranging from 70 [...] Read more.

A set of criteria to enhance mechanical performances of standard specimens (Type V, ANSI D368) made of polylactic acid (PLA) were proposed. Fused PLA deposition was conducted with nozzle temperature ranging from 180 to 230 °C and deposition plate temperature ranging from 70 to 110 °C. Optical microscopy, elastic modulus analysis and density measurement allowed emphasizing the effect of temperature field, also measured during the process, on the morphology and the mechanical characteristics of the specimen. Atomic force microscopy revealed a morphology typical of amorphous samples with globular structures. Poor interlayer adhesion was detected in the part of the specimen located at larger distance from the deposition plate, showing an elastic modulus lower than those measured in the central part (220 MPa vs. 500 MPa). The specimen crystallinity degree was below 3%. The molecular weight between entanglements was adopted as a measure of the interlayer molecular diffusion. A successful diffusion and re-entanglement of the polymer melt at the interface was the key to improving mechanical performance. A mathematical model describing the transient heat transfer during the fused PLA deposition and accounting for solidification and the nonisothermal crystallization kinetics was introduced. Simulated temperature evolutions were consistent with the experimental ones. They were related to the mechanical performances, the morphology, and the molecular weight between entanglements of the parts. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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19 pages, 12705 KiB

Open AccessArticle

Ultrasonic Welding of PBT-GF30 (70% Polybutylene Terephthalate + 30% Fiber Glass) and Expanded Polytetrafluoroethylene (e-PTFE)

by Dan Dobrotă and Sergiu Viorel Lazăr

Polymers 2021, 13(2), 298; https://doi.org/10.3390/polym13020298 - 19 Jan 2021

Cited by 6 | Viewed by 3845

Abstract

The ultrasonic welding of polymeric materials is one of the methods often used in practice. However, each couple of material subjected to ultrasonic welding is characterized by different values of technological parameters. Therefore, the main objective of the research presented in this paper [...] Read more.

The ultrasonic welding of polymeric materials is one of the methods often used in practice. However, each couple of material subjected to ultrasonic welding is characterized by different values of technological parameters. Therefore, the main objective of the research presented in this paper is to optimize the parameters for the ultrasonic welding of two materials, namely PBT-GF30 (70% polybutylene terephthalate + 30% fiber glass) and expanded polytetrafluoroethylene (e-PTFE). In this sense, the research was carried out considering a plate-type part made of PBT-GF30, which had a thickness of 2.1 mm, and a membrane-type part made of e-PTFE, with a thickness of 0.3 mm. The condition imposed on the welded joints made, namely to correspond from a technical point of view, was that the detachment pressure of the membrane should be at least 4 bar. To this end, a test device was designed. Additionally, the topography of the material layer from the plate-type part was analyzed, as well as the chemical composition and surface condition for the membrane-type part. The obtained results allowed the optimization of the following parameters: The welding force; welding time; amplitude; and holding time. All experimental results were processed using STATISTICS software, which established how each parameter influences the characteristics of welded joints. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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21 pages, 4086 KiB

Open AccessArticle

Comparison of Degradation Behavior of Newly Developed Encapsulation Materials for Photovoltaic Applications under Different Artificial Ageing Tests

by Chiara Barretta, Gernot Oreski, Sonja Feldbacher, Katharina Resch-Fauster and Roberto Pantani

Polymers 2021, 13(2), 271; https://doi.org/10.3390/polym13020271 - 15 Jan 2021

Cited by 40 | Viewed by 4553

Abstract

The main focus of this work is to investigate the degradation behavior of two newly developed encapsulants for photovoltaic applications (thermoplastic polyolefin (TPO) and polyolefin elastomer (POE)), compared to the most widely used Ethylene Vinyl Acetate (EVA) upon exposure to two different artificial [...] Read more.

The main focus of this work is to investigate the degradation behavior of two newly developed encapsulants for photovoltaic applications (thermoplastic polyolefin (TPO) and polyolefin elastomer (POE)), compared to the most widely used Ethylene Vinyl Acetate (EVA) upon exposure to two different artificial ageing tests (with and without ultraviolet (UV) irradiation). Additive composition, optical and thermal properties and chemical structure (investigated by means of Thermal Desorption Gas Chromatography coupled to Mass Spectrometry, UV-Visible-Near Infrared spectroscopy, Differential Scanning Calorimetry, Thermogravimetric Analysis and Fourier Transform-Infrared spectroscopy, respectively) of the analyzed polymers were monitored throughout the exposure to artificial ageing tests. Relevant signs of photo-oxidation were detectable for TPO after the UV test, as well as a depletion of material’s stabilizers. Signs of degradation for EVA and POE were detected when the UV dose applied was equal to 200 kW h m⁻². A novel approach is presented to derive information of oxidation induction time/dose from thermogravimetric measurements that correlate well with results obtained by using oxidation indices. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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18 pages, 5167 KiB

Open AccessArticle

Reinforced Smart Foams Produced with Time-Profiled Magnetic Fields

by Daniele Davino, Marco D’Auria, Roberto Pantani and Luigi Sorrentino

Polymers 2021, 13(1), 24; https://doi.org/10.3390/polym13010024 - 23 Dec 2020

Cited by 4 | Viewed by 1921

Abstract

Polymeric smart foams are lightweight and multifunctional porous materials that are sensitive to the magnetic field due to the presence of magnetic particles embedded in the matrix. Recently, a constant magnetic field has been exploited to align the particles along the magnetic field [...] Read more.

Polymeric smart foams are lightweight and multifunctional porous materials that are sensitive to the magnetic field due to the presence of magnetic particles embedded in the matrix. Recently, a constant magnetic field has been exploited to align the particles along the magnetic field lines during the formation of the porous structure. In this paper, a new field-structuring process was developed that makes use of a time-profiled magnetic field during the foaming process to control the geometrical features of the particles aggregates. The effects of magnetic field strength as well as the switch-on and switch-off times on the magnetoelastic behavior of the smart foams were investigated. It was proven that the alignment of the particles results in both a strong relative sensitivity to the magnetic field and a positive stress change, whose extent depends on the geometrical features of the developed aggregates. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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9 pages, 4523 KiB

Open AccessArticle

Evaluation of a Novel Nanodroplet Cutting Fluid for Diamond Turning of Optical Polymers

by Lihua Li, Hau Chung Wong and Rong Bin Lee

Polymers 2020, 12(10), 2213; https://doi.org/10.3390/polym12102213 - 27 Sep 2020

Cited by 4 | Viewed by 2356

Abstract

In this study, a novel nanodroplet cutting fluid (NDCF), consisting of emulsified water and oil nanodroplets, was developed to improve the surface quality of the single-point diamond-turned optical polymers. This developed NDCF was able to penetrate the chip–tool interface, contributing to both cooling [...] Read more.

In this study, a novel nanodroplet cutting fluid (NDCF), consisting of emulsified water and oil nanodroplets, was developed to improve the surface quality of the single-point diamond-turned optical polymers. This developed NDCF was able to penetrate the chip–tool interface, contributing to both cooling and lubricating effects. The performance of NDCF was evaluated from perspectives of the surface irregularity, roughness, and cutting force of the machined groove in a series of taper cutting experiments. Meanwhile, a high-quality optical surface was obtained and the micro-level form error was reduced in the diamond turning of a Polymethylmethacrylate (PMMA) microlens array. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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13 pages, 9670 KiB

Open AccessArticle

Physical and Morphological Properties of Tough and Transparent PMMA-Based Blends Modified with Polyrotaxane

by Akira Ishigami, Kazuki Watanabe, Takashi Kurose and Hiroshi Ito

Polymers 2020, 12(8), 1790; https://doi.org/10.3390/polym12081790 - 10 Aug 2020

Cited by 19 | Viewed by 5121

Abstract

We prepared several novel, tough, and transparent poly(methyl methacrylate) (PMMA) blends modified with polyrotaxane (PR) and evaluated their physical properties and morphologies. A styrene/methyl methacrylate/maleic anhydride (SMM) copolymer that was miscible with PMMA was used as a reactive compatibilizer to enhance interfacial adhesion [...] Read more.

We prepared several novel, tough, and transparent poly(methyl methacrylate) (PMMA) blends modified with polyrotaxane (PR) and evaluated their physical properties and morphologies. A styrene/methyl methacrylate/maleic anhydride (SMM) copolymer that was miscible with PMMA was used as a reactive compatibilizer to enhance interfacial adhesion between the matrix resin and PR. A twin-screw melt-kneading extruder was used to prepare the polymer blends, and their thermal, morphological, optical, and mechanical properties were characterized. The effect of PR was evaluated by analyzing the deformation behavior of the blends in notched three-point bending tests. A PMMA/PR blend was immiscible and appeared to be a phase-separated system. However, when SMM was added as a compatibilizer, PR was partially miscible and did not form observable PR domains. Viscosity increased, and the glass transition temperature (T_g) of the matrix resin decreased. The surface hardness of a PMMA/SMM/PR blend was only 15% lower than that of PMMA. A 2.5-fold increase in elongation at breakage was observed, and the tensile strength and Young’s modulus decreased by 16%. The PMMA/SMM/PR blend had 60% higher impact strength than PMMA in notched Charpy impact test, which indicated that the balance between stiffness and ductility was excellent. PR served as a starting point for plastic deformation in the PMMA/SMM/PR blend. We found that PR could initiate void and craze formation, even when it was finely dispersed at the nanoscale. The stress-relieving effect of PR was effective when it was tightly bound at the interfaces. The materials obtained in this study are expected to make a significant contribution to reducing the weight of the products by applying them as a replacement for glass. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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13 pages, 3079 KiB

Open AccessArticle

Systematic Investigation on the Structure-Property Relationship in Isotactic Polypropylene Films Processed via Cast Film Extrusion

by Federico Di Sacco, Markus Gahleitner, Jingbo Wang and Giuseppe Portale

Polymers 2020, 12(8), 1636; https://doi.org/10.3390/polym12081636 - 23 Jul 2020

Cited by 13 | Viewed by 4081

Abstract

The effect of cast film extrusion processing conditions, such as the chill-roll temperature, temperature of the melt, and line speed, on the structure of different isotactic polypropylene homo- and random copolymers has been investigated by means of Small- and Wide-Angle X-ray Scattering (SAXS [...] Read more.

The effect of cast film extrusion processing conditions, such as the chill-roll temperature, temperature of the melt, and line speed, on the structure of different isotactic polypropylene homo- and random copolymers has been investigated by means of Small- and Wide-Angle X-ray Scattering (SAXS and WAXS) and correlated to stiffness and haze. Stiffness and transparency have been found to be strongly dependent on the temperature of the chill-roll. Interestingly, line speed has been found to affect the total crystallinity when the chill-roll temperature is increased, while an overall minor effect of the melt temperature was found for all cast films. The polymer characteristics, defined by the catalyst nature and comonomer content, affect the final material performance, with the single-site catalyzed grades performing better in both mechanics and optics. Haze levels were found to correlate with the mesophase content rather than to α-crystallinity and to be dependent on the domain size for all grades. The remarkably low haze levels reached by the single-site grade with higher isotacticity can arise from high nucleation rate and orientational effects, which ultimately yield smaller and smoother scattering domains. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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14 pages, 5093 KiB

Open AccessArticle

Development of Polypropylene-Based Single-Polymer Composites With Blends of Amorphous Poly-Alpha-Olefin and Random Polypropylene Copolymer

by László József Varga and Tamás Bárány

Polymers 2020, 12(6), 1429; https://doi.org/10.3390/polym12061429 - 26 Jun 2020

Cited by 10 | Viewed by 4067

Abstract

We developed polypropylene-based single-polymer composites (PP-SPC) with blends of amorphous poly-alpha-olefin (APAO) and random polypropylene copolymer (rPP) as matrix material and polypropylene (PP) woven fabric as reinforcement. Our goal was to utilize the lower melting temperature of APAO/rPP blends to increase the consolidation [...] Read more.

We developed polypropylene-based single-polymer composites (PP-SPC) with blends of amorphous poly-alpha-olefin (APAO) and random polypropylene copolymer (rPP) as matrix material and polypropylene (PP) woven fabric as reinforcement. Our goal was to utilize the lower melting temperature of APAO/rPP blends to increase the consolidation of the composites and decrease the heat load of the PP reinforcement. We produced the composites by film-stacking at 160 °C, and characterized the composites with density, peel, static tensile and dynamic falling weight impact tests, and by scanning electron microscopy. The results indicate that consolidation can be enhanced by increasing the APAO content of the matrix. We found that the APAO content of 50% is optimal for tensile properties. With increasing APAO content, the perforation energy decreased, but even the well-consolidated composites showed very high perforation energy. In the case of a pure APAO matrix, fiber content can be increased up to 80 wt% without a severe loss of consolidation, resulting in good tensile properties. The PP-SPCs developed possessed excellent mechanical properties, and well-consolidated composites can be produced with APAO/rPP blends as a matrix with high fiber content. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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18 pages, 4543 KiB

Open AccessArticle

Influence of Different Types of Peroxides on the Long-Chain Branching of PP via Reactive Extrusion

by Sascha Stanic, Gergö Gottlieb, Thomas Koch, Lukas Göpperl, Klaus Schmid, Simone Knaus and Vasiliki-Maria Archodoulaki

Polymers 2020, 12(4), 886; https://doi.org/10.3390/polym12040886 - 11 Apr 2020

Cited by 25 | Viewed by 8448

Abstract

Long-chain branching (LCB) is known as a suitable method to increase the melt strength behavior of linear polypropylene (PP), which is a fundamental weakness of this material. This enables the modification of various properties of PP, which can then be used—in the case [...] Read more.

Long-chain branching (LCB) is known as a suitable method to increase the melt strength behavior of linear polypropylene (PP), which is a fundamental weakness of this material. This enables the modification of various properties of PP, which can then be used—in the case of PP recyclates—as a practical “upcycling” method. In this study, the effect of five different peroxides and their effectiveness in building LCB as well as the obtained mechanical properties were studied. A single screw extruder at different temperatures (180 and 240 °C) was used, and long-chain branched polypropylene (PP-LCB) was prepared via reactive extrusion by directly mixing the peroxides. The peroxides used were dimyristyl peroxydicarbonate (PODIC C126), tert-butylperoxy isopropylcarbonate (BIC), tert-Butylperoxy 2-ethylhexyl carbonate (BEC), tert-amylperoxy 2-ethylhexylcarbonate (AEC), and dilauroyl peroxide (LP), all with a concentration of 20 mmol/kg. The influence of the temperature on the competitive prevalent reactions of degradation and branching was documented via melt mass-flow rate (MFR), rheology measurements, and gel permeation chromatography (GPC). However, via extensional rheology, strain hardening could be observed in all cases and the mechanical properties could be maintained or even improved. Particularly, PODIC C126 and LP signaled a promising possibility for LCB in this study. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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Review

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36 pages, 3994 KiB

Open AccessReview

Antiplasticization of Polymer Materials: Structural Aspects and Effects on Mechanical and Diffusion-Controlled Properties

by Leno Mascia, Yannis Kouparitsas, Davide Nocita and Xujin Bao

Polymers 2020, 12(4), 769; https://doi.org/10.3390/polym12040769 - 1 Apr 2020

Cited by 47 | Viewed by 7648

Abstract

Antiplasticization of glassy polymers, arising from the addition of small amounts of plasticizer, was examined to highlight the developments that have taken place over the last few decades, aiming to fill gaps of knowledge in the large number of disjointed publications. The analysis [...] Read more.

Antiplasticization of glassy polymers, arising from the addition of small amounts of plasticizer, was examined to highlight the developments that have taken place over the last few decades, aiming to fill gaps of knowledge in the large number of disjointed publications. The analysis includes the role of polymer/plasticizer molecular interactions and the conditions leading to the cross-over from antiplasticization to plasticization. This was based on molecular dynamics considerations of thermal transitions and related relaxation spectra, alongside the deviation of free volumes from the additivity rule. Useful insights were gained from an analysis of data on molecular glasses, including the implications of the glass fragility concept. The effects of molecular packing resulting from antiplasticization are also discussed in the context of physical ageing. These include considerations on the effects on mechanical properties and diffusion-controlled behaviour. Some peculiar features of antiplasticization regarding changes in Tg were probed and the effects of water were examined, both as a single component and in combination with other plasticizers to illustrate the role of intermolecular forces. The analysis has also brought to light the shortcomings of existing theories for disregarding the dual cross-over from antiplasticization to plasticization with respect to modulus variation with temperature and for not addressing failure related properties, such as yielding, crazing and fracture toughness. Full article

(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers II)

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